Plasma enhanced chemical vapor deposition apparatus and method for forming nitride layer using the same

ABSTRACT

A plasma enhanced chemical vapor deposition apparatus and a method of forming a nitride layer using the same, wherein the plasma enhanced CVD apparatus includes a process chamber including an upper chamber with a dome shape, a lower chamber, and an insulator therebetween, a gas distributing ring, a susceptor for supporting a wafer and heating the process chamber, a plasma compensation ring surrounding the susceptor, a vacuum pump and an electric power source connected to the process chamber. The gas distributing ring has a plurality of upwardly inclined nozzles, allowing upward distribution of reactive gases. The method of forming a nitride layer includes forming a protective film on inner walls of a process chamber, the protective film having at least two layers of differeing dielectric constant, and sequentially supplying reactive gases to the process chamber. A nitride layer formed thereby has low hydrogen content, good density and oxidation resistance.

This application is a DIVISION of application Ser. No. 10/277,801, filedOct. 23, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a chemical vapor deposition (CVD)apparatus and a method for forming a nitride layer using the same. Moreparticularly, the present invention relates to a plasma enhancedchemical vapor deposition (PECVD) apparatus used for fabricating asemiconductor device and a method of forming a nitride layer using thesame.

2. Description of the Related Art

There is a wide range of uses for a nitride layer in the field ofsemiconductor devices. One use of a nitride layer is as an etching maskin an etching process for forming metal patterns from an aluminum layeror a titanium layer, and as a protection layer for preventing asemiconductor device from being contaminated. Another use of a nitridelayer is as an insulator when formed between conductive layers. Stillanother use of a nitride layer is as an etch-stopping layer to detect anend point in an etching process.

Typically, a nitride layer is formed by a method of PECVD, as disclosedin the prior art. The prior art discloses that a thin film is depositedby introducing a process gas and a carrier gas into a process chambersustaining a temperature of about 350-450° C. and a pressure of about1-10 Torr. Then, a high frequency voltage of about 50-200 W at a sourceradio frequency of 13.56 MHz is applied to the process chamber to createa plasma atmosphere therein.

The method disclosed in the prior art has an advantage that deviceoperation characteristics are not deteriorated because the process isperformed at low temperature of about 350-450° C. However, the methodalso has many disadvantages, such as high degree of hydrogen content,low film density, weak oxidation resistance and film lifting, which arecaused by high thermal stress after the thin film undergoes subsequentheat treatment processes.

FIG. 1 shows a conventional plasma enhanced CVD apparatus. Theconventional plasma enhanced CVD apparatus includes a cylinder-typeprocess chamber that comprises an upper chamber 10, a lower chamber 12and an insulator 14 inserted between the upper chamber 10 and the lowerchamber 12.

The upper chamber 10 and the lower chamber 12 serve as an upperelectrode and a lower electrode, respectively, so that an electric fieldmay be generated therebetween.

An external end of a gas supply pipe 18 located outside the processchamber connected to a process gas supply source 20, also locatedoutside the process chamber, is externally inserted into the processchamber through a top portion of the upper chamber 10. The other end, aninternal end, of the gas supply pipe 18 located inside the processchamber is connected to a gas distributing plate 16.

FIG. 2 depicts a perspective view of a gas distributor in accordancewith the conventional PECVD apparatus.

As shown in FIG. 2, the gas distributing plate 16 is a circular disk andhas a plurality of gas distributing nozzles 17 at a bottom surfacethereof, for facilitating downward ejection of process gases from thenozzles 17 toward a bottom of the lower chamber 12.

As shown in FIG. 1, the conventional plasma enhanced CVD apparatusfurther includes a rotating shaft 22 externally inserted into theprocess chamber through the bottom of the lower chamber 12. An externalend of the rotating shaft 22 is connected to a rotating driving source(not shown) for being rotated. The driving source is located outside theprocess chamber. A susceptor 24 formed of AIN is installed inside theprocess chamber and connected to an internal end of the rotating shaft22 to support a wafer 26. Further, The susceptor 24 has a heater (notshown) embedded therein to heat the wafer 26 placed thereon to apredetermined temperature and to control an internal temperature of theprocess chamber.

Further, a pumping pipe 32 is connected to the bottom of the lowerchamber 12 to control an internal pressure of the process chamber and avacuum pump 30 is connected to the pumping pipe 32.

Still further, the lower chamber 12 is connected to a loadlock chamber28 at side surface thereof, in which the wafer 26 is placed before beingloaded to or after being unloaded from the susceptor 24.

FIG. 3 illustrates a block diagram to explain operation of theconventional plasma enhanced CVD apparatus and a method of forming anitride layer using the same.

First, a protective film such as an oxide layer having a dielectricconstant of about 3.8-3.9 or a nitride layer having a dielectricconstant of about 7.5 is coated on inner walls of the process chamberduring a step S2. Ions in plasma tend to move toward the inner walls ofthe process chamber due to capacitance of the process chamber walls, sothat an initial nitride layer formed at the beginning of a depositionprocess has low uniformity in thickness. The protective film on theinner walls of the process chamber serves to prevent the initial nitridelayer from having a low uniformity in thickness.

The protective film formed of the oxide layer may be formed by supplyinga process gas such as nitrogen oxide N₂O or nitrogen monoxide NO and acarrier gas of nitrogen N₂ to the process chamber and creating a plasmaatmosphere in the process chamber.

The protective film formed of the nitride layer may be formed bysupplying process gases of silane and ammonia to the process chamber andthen adjusting the internal temperature and pressure of the processchamber, and applying a high frequency power to the process chamber tocreate a plasma atmosphere therein.

Next, during a step S4, a sheet of wafers is loaded onto the susceptor24 in the process chamber by a moving means such as a robot arm.

The process chamber maintains an internal pressure of about 0.5-0.7mTorr after activation of the vacuum pump 30, and an internaltemperature of about 400° C. after activation of the heater embeddedunder the susceptor 24. The heater also causes the temperature of thewafer 26 on the susceptor 24 to become about 400° C.

Next, the susceptor 24 is rotated at a predetermined speed by therotating shaft 22.

Next, during a step S6, ammonia and silane as process gases are suppliedto the process chamber through the process gas supply pipe 18 and thegas distributing plate 16, and electric power of about 500-1000 W isapplied to the upper chamber 10 and the lower chamber 12.

During the step S6, the process gases are converted to plasma due to anelectric field induced by the electric power applied to the upperchamber 10 and the lower chamber 12, so that a plasma atmosphere iscreated in the process chamber.

Next, during a step S8, ions in the plasma atmosphere are deposited onthe wafer 26, thereby forming a nitride layer on the wafer 26 after apredetermined time delay.

Next, during a step S10, the process gas supply and the electric powersupply to the process chamber stop.

Next, during a step S12, the wafer 26 is unloaded from the susceptor 24and shifted to the loadlock chamber 28 by the moving means of the robotarm.

Next, during a step S14, particles and process gases remaining in theprocess chamber are forced to be discharged by initiating a vacuum pump30 and the inner part of the process chamber is cleaned by a cleaninggas of Argon.

Next, the steps S2-S14 are repeated about 25 times, thereby forming anitride layer on each of 25 wafers on a sheet.

Finally, after the 25 wafers are coated with the nitride layer, theinner part of the process chamber undergoes a plasma etching cleaningprocess in a step S16, so that the protective film coated on the innerwalls and components in the process chamber, as well as byproducts, areremoved. As a result, the process chamber is completely cleaned. Theplasma etching cleaning process of the step 16 is performed by supplyinga gas of nitrogen trifluoride NF₃ and a carrier gas of Ar to the processchamber and converting the same into plasma.

The conventional plasma enhanced CVD apparatus shown in FIG. 1 has somedrawbacks.

First, the plasma formed by the conventional plasma enhanced CVDapparatus has very low intensity. The conventional plasma enhanced CVDapparatus has a cylinder-type upper chamber, allowing the plasma formedin the process chamber to spread throughout the inside of thecylinder-type process chamber. Therefore, the intensity of the plasmadecreases.

Also, there is a space in the process chamber between the inner wall ofthe chamber and the susceptor, where the plasma may also spread, therebyfurther decreasing the plasma intensity.

Second, a nitride layer formed using the conventional plasma enhancedCVD apparatus has poor quality and characteristics. In the conventionalplasma enhanced CVD apparatus, the gas distributing plate ejects theprocess gases directly downward toward the bottom of the chamber. Sincethe gases cannot be completely converted into plasma, the gases aredeposited on the wafer. Accordingly, non-reactive particles may bedeposited on the wafer, thereby lowering the quality of the nitridelayer.

Further, the protective films formed on the inner walls of the processchamber have a high dielectric constant (for example, about 3.8-3.9 incase of an oxide layer, about 7.5 in case of a nitride layer), so thatcapacitance of the inner walls of the process chamber is still high.Therefore, ions in plasma are insufficiently deposited on the wafer,thereby forming a nitride layer with poor uniformity in thicknessbecause ions in plasma move toward the inner walls due to thecapacitance thereof.

Still further, the process gases of silane and ammonia aresimultaneously supplied to the process chamber. However, the silane gasis occasionally transformed into plasma earlier than the ammonia gas.The advanced reaction causes formation of particles containingpolysilicon. These particles are deposited on the wafer, resulting indeterioration of the quality and characteristics of the nitride layer.

Still further, in accordance with the conventional plasma enhanced CVDmethod, the nitride layer formed at a relatively low temperature of 400°C. is easily lifted by high thermal stress caused by subsequent heattreatments. The nitride layer in accordance with the conventional methodis further limited by having a high degree of hydrogen content, low filmdensity and weak oxidation resistance.

SUMMARY OF THE INVENTION

It is therefore a feature of an embodiment of the present invention toprovide a plasma enhanced CVD apparatus capable of forming a nitridelayer of high quality by preventing a decrease in plasma intensityduring a deposition process and a method of forming a nitride layerusing the same.

It is therefore another feature of an embodiment of the presentinvention to provide a plasma enhanced CVD apparatus capable ofpreventing non-reactive particles from being formed and deposited on awafer by completely converting reactive gases to plasma and a method offorming a nitride layer using the same.

It is therefore another feature of an embodiment of the presentinvention to provide a plasma enhanced CVD apparatus capable of reducingcapacitance of inner walls of a process chamber, thereby forming anitride layer of high quality and a method of forming a nitride layerusing the same.

It is therefore still another feature of an embodiment of the presentinvention to provide a plasma enhanced CVD apparatus capable of forminga nitride layer with a low degree of hydrogen content, high density andstrong oxidation resistance, and a method of forming a nitride layerusing the same.

According to one aspect of the preset invention, a preferred embodimentof the present invention provides a plasma enahnced CVD apparatus. Theapparatus includes a process chamber including an upper chamber with adome shape, a lower chamber, and an insulator placed between the upperchamber and the lower chamber, a gas distributing ring installed in theprocess chamber for ejecting a gas in an upward direction inside theprocess chamber, a susceptor installed below the gas distributing ringfor supporting a wafer thereon, and having a heater for controlling atemperature of the wafer and an internal temperature of the processchamber, a plasma compensation ring installed at an upper part of sidewalls of the susceptor, a vacuum pump connected to the process chamber,and an electric power source connected to the upper chamber and thelower chamber.

Preferably, the gas distributing ring has a plurality of nozzles atinner walls thereof, wherein each of the plurality of nozzles isupwardly sloped with an inclination of, for example, 30-60 degrees,thereby allowing upward distribution of a gas. The gas distributing ringand/or the plasma compensation ring may be made of stainless steel.

The plasma enhanced CVD apparatus may further include a loadlock chamberconnected to the process chamber.

The susceptor is preferably coated with Al₂O₃, so that the susceptor isnot etched by nitrogen trifluoride plasma during a plasma etchingcleaning process.

According to another aspect of the preset invention, a preferredembodiment of the present invention provides a method of forming anitride layer using a plasma enhanced CVD apparatus. The method includesloading a wafer onto a susceptor, supplying a first reactive gascontaining nitrogen N₂ to a process chamber, leaving the wafer intactfor a first delay time, forming a basic layer on the water by convertingthe first reactive gas into plasma which is created by applying electricpower to the process chamber, leaving the wafer intact for a seconddelay time, forming a nitride layer on the wafer having the basic layerthereon by supplying a second reactive gas to the process chamber andconverting the second reactive gas into plasma, leaving the wafer intactfor a third delay time, stopping the supply of the first and secondreactive gases to the process chamber, leaving the wafer intact for afourth delay time, stopping applying the electric power, and unloadingthe wafer from the susceptor.

The wafer may be loaded and unloaded through a loadlock chamberconnected to the process chamber so that the wafer is not exposed toair, thereby preventing oxidation of the wafer.

Ammonia and silane may be used as the first reactive gas and the secondreactive gas, respectively.

Forming the nitride layer is preferably performed in the process chamberhaving an internal temperature of 580-670° C., an internal pressure of0.5-0.7 mTorr, and an electric power applied thereto of 100-700 W.

A protective film may be formed on inner walls of the process chamberbefore loading the wafer, the protective film preferably being formed ofat least two layers (i.e. an oxide layer and a nitride layer), each ofwhich has a dielectric constant different from the others. For example,an oxide layer may be formed on the inner walls of the process chamber,and a nitride layer may be formed on the oxide layer.

The oxide layer as the protective film may be formed by supplyingnitrogen oxygen gas N₂O or NO to the process chamber and converting thesame into plasma. The nitride layer as the protective film may formed byintroducing ammonia gas and silane gas into the process chamber andconverting the same gases into plasma.

After unloading the wafer, the process chamber may be vacuumed tocompulsorily exhaust a gas remaining in the process chamber and acleaning gas may be supplied to the process chamber.

After unloading the wafer, plasma etching cleaning to clean inner wallsof the process chamber and components installed in the process chambermay be performed. The plasma etching cleaning is preferably performed bysupplying nitrogen trifluoride gas to the process chamber and convertingthe same gas into plasma.

These and other aspects, features, and advantages of the presentinvention will become more apparent from the following detaileddescription of preferred embodiments, which is to be read in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic view of a conventional plasma enhancedCVD apparatus;

FIG. 2 illustrates a perspective view of a gas distributor in accordancewith the conventional plasma enhanced CVD apparatus;

FIG. 3 depicts a block diagram illustrating a method of forming anitride layer using a conventional plasma enhanced CVD apparatus;

FIG. 4 illustrates a schematic view of a plasma enhanced CVD apparatusin accordance with the present invention;

FIG. 5 illustrates a partial perspective view of a gas distributing ringin accordance with the present invention;

FIG. 6 depicts a block diagram illustrating a method of forming anitride layer using a plasma enhanced CVD apparatus in accordance withthe present invention;

FIG. 7 depicts a graph illustrating thickness uniformity of a nitridelayer which is formed in a process chamber having a protective filmformed of one among nitride, oxide and oxide/nitride on inner wallsthereof; and

FIG. 8 depicts a graph illustrating intensity of thermal stress ofnitride layers formed by varying internal temperature of the processchamber.

DETAILED DESCRIPTION OF THE INVENTION

Korean Patent Application No. 2001-66104, filed on Oct. 25, 2001, andentitled: “Plasma Enhanced Chemical Vapor Deposition Apparatus AndMethod For Forming Nitride Layer Using The Same,” is incorporated byreference herein in its entirety.

FIG. 4 illustrates a schematic view of a plasma enhanced CVD apparatusin accordance with the present invention. As shown in FIG. 4, theapparatus includes a process chamber in which a nitride layer would beformed, a gas supply pipe 46, a susceptor 52, a plasma compensation ring54, a vacuum pump 60, and electric power source.

The process chamber comprises an upper chamber 40 with a dome shape, acylinder-type lower chamber 42, and a gas distributing ring 44 made ofstainless steel. The gas distributing ring 44 is placed between theupper chamber 40 and the lower chamber 42.

The upper chamber 40 and the lower chamber 42 serve as an upperelectrode and a lower electrode, respectively, thereby forming anelectric field in the process chamber by applying electric powerthereto.

It is noted that the upper chamber 40 has a dome shape, so that plasmaintensity does not decrease due to the spreading of the plasmathroughout the cylindrical-type upper chamber as in the prior art.

Insulation between the upper chamber 40 and the lower chamber 42 may beachieved by placing insulating materials or components therebetween,instead of the gas distributing ring 44. The gas distributing ring 44may be employed inside the process chamber by being supported with afixing means.

A process gas supply source 48 is connected to one end of the gas supplypipe 46 external to the process chamber. The other end of the gas supplypipe 46 is connected to the gas distributing ring 44 to allow processgas to be supplied to the gas distributing ring 44.

FIG. 4 shows that a diameter of the gas distributing ring 44 is the sameas the diameter of the cylindrical-type lower chamber 42 and a bottom ofthe dome-shaped upper chamber 40. Therefore, the gas distributing ring44 may be properly or precisely fixed between the upper chamber 40 andthe lower chamber 42. Further, as may be seen in FIG. 5, the gasdistributing ring 44 has a plurality of nozzles 45 at an inner sidewallthereof. Each of the plurality of nozzles 45 is upwardly inclined at aninclination angle of about 30-60 degrees, and more preferably about 45degrees. Therefore, the reactive gas may be ejected in an upwarddirection from the nozzles 45 at a predetermined angle of inclination,so that a retention time of the reactive gas in the process chamber isincreased. As a result, the reactive gas is almost entirely convertedinto plasma, thereby reducing formation of particles on the wafer.

A rotating shaft 50 is externally inserted into the lower chamber 42through a bottom of the lower chamber 42. The rotating shaft 50 isrotated by driving gear (not shown). Further, a susceptor 52 madepreferably of AIN is installed on the top of the rotating shaft 50 inthe process chamber. The susceptor 52 includes an embedded heater forheating a wafer 56 placed thereon and for adjusting an internaltemperature of the process chamber to about 650° C. A refractory metallayer such as aluminum oxide Al₂O₃ may be coated on a surface of thesusceptor 52, thereby preventing the susceptor 52 from being etched byplasma created in the process chamber under a high temperature.

The plasma compensation ring 54 surrounds the susceptor 52 at an upperportion of sidewalls of the susceptor 52. The plasma compensation ring54 reduces a distance between the susceptor 52 and the inner walls ofthe lower chamber 42, thereby preventing the plasma from spreading to aspace between the susceptor 52 and the inner wall of the lower chamber42.

The plasma enhanced CVD apparatus in accordance with the presentinvention may further include a loadlock chamber 58 at one side of thelower chamber 42. Wafers are placed in the loadlock chamber 58 beforebeing loaded to the susceptor 52 or after being unloaded from thesusceptor 52.

The vacuum pump 60 is connected to the lower chamber 42 for controllinginternal pressure of the process chamber. The vacuum pump 60 isconnected to the lower chamber 42 by means of a pumping pipe 62 throughthe bottom of the lower chamber 42.

FIG. 6 depicts a block diagram illustrating a method of forming anitride layer using the plasma enhanced CVD apparatus in accordance witha preferred embodiment of the present invention.

First, in step S20, a protective film is formed on inner walls of theprocess chamber. The protective film may be formed of a double layerincluding a nitride layer having a dielectric constant A, about 3.8-3.9,and an oxide layer having a dielectric constant B, about 7.5. Theprotective film prevents ions in plasma from moving toward the innerwalls of the process chamber, thereby forming an initial nitride layerwith excellent uniformity of thickness. The protective film formed inaccordance with the present invention has a dielectric constant C, about2.5, which is calculated as follows:

 Dielectric constant C=(A×B)/(A+B)

The protective film in accordance with the present invention has adielectric constant much lower than that of the conventional protectivefilm. Therefore, the protective film of the present inventioneffectively prevents the ions in plasma from moving toward the innerwalls of the process chamber.

The oxide layer comprising the protective film of the present inventionis formed by supplying a process chamber with a carrier gas of nitrogenN₂ and a reactive gas of nitrogen oxygen gas N₂O or NO, and thenadjusting factors to create a plasma atmosphere. The factors includeinternal pressure and internal temperature of the process chamber andelectric power.

The nitride layer comprising the protective film of the presentinvention is formed by supplying a process chamber with nitrogen N₂ as acarrier gas and silane and ammonia as reactive gases, and then creatinga plasma atmosphere in the process chamber. The plasma atmosphere iscreated by adjusting various factors such as internal pressure andtemperature of the process chamber and electric power.

Next, in step S22, a wafer 56 is loaded on the susceptor 52 by a movingmeans such as a robot arm. The wafer 56 is sustained on the loadlockchamber 58 having a pressure of 200 mTorr before being loaded onto thesusceptor 52. Although the wafer 56 is coated with an easily oxidizablelayer such as tungsten, the wafer 56 is free from being oxidized becauseit is not exposed to air.

During the step 22, as the vacuum pump 60 is initiated, the processchamber having a susceptor 52 on which the wafer 56 is loaded isvacuumed, thereby maintaining an internal pressure of about 0.5-0.7mTorr. Further, heating the susceptor 52 by a heater raises thetemperature of the wafer 56 and the internal temperature of the processchamber to about 580-670° C., respectively. During the step S22, thesusceptor 52 connected to the rotating shaft 50 is being rotated.

Next, in step 24, ammonia as a reactive gas is supplied to the processchamber from the gas supply source 48 through the gas supply pipe 46 andthe gas distributing ring 44 at 200 SCCM (standard cubic centimeterminute).

Next, in step S26, there is a first delay time of about 10 seconds. Thewafer 26 is left intact in the process chamber for the first delay time.

Next, in step S28, an electric power of 100-700 W is applied to theupper chamber 40 and the lower chamber 42 serving as the upper electrodeand the lower electrode, respectively, so that the ammonia is convertedinto plasma. During the step S28, the ammonia is upwardly ejected at aninclination angle of about 45 degrees toward the center of the processchamber through the nozzles 45 of the gas distributing ring 44.Therefore, enough time is allowed for the ammonia gas to be convertedinto plasma. At this time, nitrogen contained in the ammonia gas isdeposited on the wafer 56, thereby forming a basic layer of nitrogen.The basic layer serves as a seed to form a nitride layer. A nitridelayer to be formed on the basic layer has high quality in aspects of thethickness uniformity, reflectance index and absorption index. Further,ion bombardment to the wafer is avoided due to the low electric power ofabout 100 W-700 W applied while creating a plasma atmosphere in theprocess chamber. The upper chamber 40 has a dome shape and the susceptor52 has a plasma compensation ring 54, thereby increasing plasmaintensity of ammonia in the process chamber.

Next, in step S30, there is a second delay time of about 10 seconds. Thewafer is left intact in the process chamber for the second delay time.

Next, in step S32, the silane gas is supplied to the process chamber at70-100 SCCM through the gas distributing ring 44 and the gas supply pipe46 from the gas supply source 48.

During the step S32, the silane gas is converted into plasma and reactedwith the ammonia plasma created in advance, thereby forming a nitridelayer Si₃N₄ and forming H₂ gas as a byproduct. Thus, the hydrogen gasshould be discharged out of the process chamber.

In the step S32, the process chamber maintains a high internaltemperature of 580-670° C., so that the nitride layer formed in step S32has many advantages. That is, the nitride layer formed at the hightemperature is hardly lifted and has properties of low hydrogen content,high density and strong oxidation resistance.

In the step S32, the silane gas is ejected upward with an inclination of45 degrees toward the center of the process chamber through the gasdistributing ring 44. Thus, retention time is long enough for theammonia gas to completely react with the silane gas, thereby preventingparticles containing polysilicon from being formed and deposited on thewafer.

Further, the upper chamber 40 is formed to have a dome shape and theplasma compensation ring 54 is installed to surround the susceptor 52 atupper portions of sides thereof. Therefore, the plasma intensity of thesilane is not decreased, and a nitride layer having good uniformity ofthickness may be formed.

Next, in step S34, there is a third delay time of about 10 seconds afterstep S32. The wafer is left intact in the process chamber during thethird delay time.

Next, in step S36, supply of the reactive gases of ammonia and silanestops.

Next, in step S38, there is a forth delay time of about 10 seconds. Thewafer is left intact in the process chamber during the fourth delaytime. During the step S38, the ammonia gas plasma and the silane gasplasma remaining in the process chamber are completely reacted with eachother, thereby preventing reactive particles from being deposited ontothe wafer.

Next, in step S40, power supply to the upper chamber 40 and the lowerchamber 42 stops.

Next, in step S42, the wafer 56 having the nitride layer thereon isunloaded from the susceptor 52 and transferred to the loadlock chamber58.

Next, in step S44, the process chamber is vacuumed by means of thevacuum pump 60, and nitrogen gases are supplied to the process chamber,so that the byproducts and non-reactive gases remaining in the processchamber are completely removed, thereby cleaning the process chamber.

The steps S20-S44 are repeatedly performed, up to about 25 times, sothat 25 wafers may be deposited with the nitride layers.

Finally, in step S46, a plasma etching cleaning process is performed tocompletely clean the process chamber. That is, a mixed gas of nitrogentrifluoride NF₃ as a reactive gas and Argon as a carrier gas is suppliedto the process chamber and the mixed gas is transformed into plasma.During the step S46, the protective film deposited on the inner walls ofthe process chamber and other components in the process chamber isetched away by the plasma of the mixed gas, thereby completely cleaningthe process chamber.

During the step S46, a temperature of about 650° C. is maintained, sothat particles may be generated because the susceptor 52 made of AIN canbe etched at that temperature. However, in accordance with an embodimentof the present invention, the susceptor 52 is coated with aluminum oxideAl₂O₃, thereby preventing particles from being formed during the plasmaetching cleaning process.

Now, advantages of the present invention will be described below basedon various experiments.

First Experiment

A first experiment was performed as follows, and the results are listedin table 1. Nitride layers were formed while varying an internaltemperature of the process chamber, i.e., 400° C., 450° C., 550° C.,600° C. and 650° C., while other conditions remained fixed. That is, theother conditions such as process gas, protective film and internalpressure of the process chamber were the same as those in the stepsS20-S46 described above. In table 1, the nitride layers formed attemperatures of 600° C. and 650° C. are referred to as a firstembodiment and a second embodiment, respectively. The nitride layersformed at temperatures of 400° C., 450° C., and 550° C. are referred toas a first comparative example, a second comparative example and a thirdcomparative example, respectively.

Each of the nitride layers was formed to have reflection index R & I outof 1.9, 1.94, 1.98, 2.03 or 2.1 against a light source having awavelength of 673 nm.

A frequency of occurrences of a popping phenomenon, i.e., the nitridelayer being protruded, lifted or popped, was measured. The results ofthe popping frequency are indicated in Table 1.

TABLE 1 R&I Temp. 1.86 1.9 1.94 1.98 2.03 2.1 400° C. — — — 100 — —(1^(st) comparative example) 450° C. — 16 — — — — (2^(nd) comparativeexample) 550° C. — — — — 10 — (3^(rd) comparative example) 600° C. 2 3 00 0 0 (1^(st) embodiment) 650° C. 0 0 0 0 0 0 (2^(nd) embodiment)

As shown in table 1, the first comparative example indicates that 100nitride layers having R&I 1.98 were popped. The second comparativeexample indicates that 16 nitride layers having R&I 1.9 were popped. Thethird comparative example indicates that 10 nitride layers having R&I1.98 were popped.

However, the first embodiment of the present invention indicates thatonly 5 nitride layers were popped, and the second embodiment of thepresent invention indicates no popped nitride layers at al.

Second Experiment

Next, a second experiment was performed, and the results are listed intable 2. The nitride layers were formed under the same conditions as inthe first experiment, and a hydrogen content of each nitride layer wasmeasured.

In table 2, the nitride layers formed at temperatures of 600° C. and650° C. are referred to as a third embodiment and a fourth embodiment,respectively. The nitride layers formed at temperatures of 400° C., 450°C., and 550° C. are referred to as a fourth comparative example, a fifthcomparative example and a sixth comparative example, respectively.

TABLE 2 R&I Temp. 1.86 1.9 1.94 1.98 2.03 2.1 400° C. — — — 10.5 — —(4^(th) comparative example) 450° C. — 11.6 — — — — (5^(th) comparativeexample) 550° C. — — — — 7.5 — (6^(th) comparative example) 600° C. 7.06.9 6.8 — 5.8 5.4 (3^(rd) embodiment) 650° C. 0 5.5 5.3 4.8 3.8 4.0(4^(th) embodiment)

The fourth comparative example indicates a hydrogen content of 10.5atoms/cm³. Further, 11.6 atoms/cm³ and 7.5 atoms/cm³ of hydrogen contentwere detected in the fifth and the sixth comparative examples,respectively.

In the nitride layers formed in accordance with the third embodiment ofthe present invention, 7.0 atoms/cm³, 6.9 atoms/cm³, 6.8 atoms/cm³, 5.8atoms/cm³ and 5.4 atoms/cm³ of hydrogen content were detected. Further,5.5 atoms/cm³, 5.3 atoms/cm³, 4.8 atoms/cm³, 3.8 atoms/cm³ and 4.0atoms/cm³ of hydrogen content were detected in the nitride layers formedin accordance with the fourth embodiment of the present invention.

Therefore, table 2 confirms that the nitride layers formed in accordancewith preferred embodiments of the present invention contain relativelylow hydrogen content in comparison with the third to sixth comparativeexamples.

Third Experiment

The third experiment relates to the uniformity of thickness of thenitride layers. Nitride layers formed in accordance with seventh andeighth comparative examples are formed under nearly the same conditionsas the preferred embodiments of the present invention, i.e., the stepsS20-S46, except for a condition of the protective film formed on innerwalls of the process chamber. The nitride layer formed in accordancewith the seventh comparative example is formed using a process chamberhaving a protective film of nitride. The nitride layer in accordancewith the eighth comparative example is formed using a process chamberhaving a protective film of oxide. The nitride layer formed inaccordance with a fifth embodiment of the present invention is formedusing a process chamber having a protective film formed of a doublelayer of an oxide layer and a nitride layer.

FIG. 7 shows the thickness and uniformity of the nitride layers formedin accordance with the seventh comparative example, the eighthcomparative example and the fifth embodiment. As shown in FIG. 7, afirst nitride layer formed in both the seventh and eighth comparativeexample is much thicker than subsequently formed nitride layers.However, thickness of a first nitride layer formed in accordance withthe fifth embodiment is practically the same as the thickness of nitridelayers subsequently formed in accordance with the fifth embodiment.Therefore, the third experiment confirms that the present inventionprovides a nitride layer having good uniformity of thickness.

Fourth Experiment

The fourth experiment relates to a characteristic of thermal stress.Nitride layers were formed while varying a temperature of the processchamber, while other conditions remained the same as those in the stepsS20-S46. The nitride layers formed at each temperature of 400° C., 550°C., 600° C., and 650° C. are referred to as a ninth comparative example,a tenth comparative example, a sixth embodiment and a seventhembodiment, respectively. In the fourth experiment, after formation ofthe nitride layers, the nitride layers undergo heat treatments withgreat temperature variations from 0° C. to 900° C. and thermal stress isobserved.

FIG. 8 shows the results of the fourth experiment. The nitride layersformed in accordance with the ninth and tenth comparative examples showrelatively great fluctuation ranges in thermal stress compared with thatof the nitride layers formed in accordance with the sixth and theseventh embodiments of the present invention. Accordingly, it is notedthat the nitride layers formed in accordance with the embodiments of thepresent invention are thermally stable with narrow fluctuation range ofthe thermal stress.

Preferred embodiments of the present invention have been disclosedherein and, although specific terms are employed, they are used in ageneric and descriptive sense only and not for purpose of limitation.Accordingly, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made without departingfrom the spirit and scope of the present invention as set forth in thefollowing claims.

What is claimed is:
 1. A method of forming a nitride layer using aplasma enhanced CVD comprising: loading a wafer onto a susceptor;supplying a first reactive gas containing nitrogen N₂ to a processchamber; leaving the wafer intact for a first delay time; forming abasic layer on the wafer by converting the first reactive gas intoplasma which is created by applying electric power to the processchamber; leaving the wafer intact for a second delay time; forming anitride layer on the wafer having the basic layer thereon by supplying asecond reactive gas to the process chamber and converting the secondreactive gas into plasma; leaving the wafer intact for a third delaytime; stopping the supply of the first and second reactive gases to theprocess chamber; leaving the wafer intact for a fourth delay time;stopping applying the electric power; and unloading the wafer from thesusceptor.
 2. The method as claimed in claim 1, wherein loading andunloading the wafer are performed through a loadlock chamber connectedto the process chamber.
 3. The method as claimed in claim 1, whereinammonia is used as the first reactive gas and silane is used as thesecond reactive gas.
 4. The method as claimed in claim 1, whereinforming the nitride layer is performed in the process chamber having aninternal temperature of 580-670° C., an internal pressure of 0.5-0.7mTorr and an electric power applied thereto of 100-700 W.
 5. The methodas claimed in claim 1, further comprising forming a protective film oninner walls of the process chamber before loading the wafer, theprotective film being formed of at least two layers each of which has adielectric constant different from the others.
 6. The method as claimedin claim 5, wherein forming the protective film includes forming anoxide layer on the inner walls of the process chamber and forming anitride layer on the oxide layer.
 7. The method as claimed in claim 6,wherein forming the oxide layer is performed by supplying nitrogenoxygen gas to the process chamber and converting the same in plasma. 8.The method as claimed in claim 6, wherein forming the nitride layer isperformed by introducing ammonia gas and silane gas into the processchamber and converting the same gases into plasma.
 9. The method asclaimed in claim 1, further comprising vacuuming the process chamber tocompulsorily exhaust a gas remaining in the process chamber andsupplying a cleaning gas to the process chamber after unloading thewafer.
 10. The method as claimed in claim 1, further comprising plasmaetching cleaning to clean inner walls of the process chamber andcomponents installed in the process chamber after unloading the wafer.11. The method as claimed in claim 10, wherein the plasma etchingcleaning is performed by supplying nitrogen trifluoride gas to theprocess chamber and converting the same gas into plasma.